On Fri 23-12-11 20:59:12, Wu Fengguang wrote:
> The accounting code will be compiled in by default (CONFIG_READAHEAD_STATS=y),
> and will remain inactive by default.
>
> It can be runtime enabled/disabled through the debugfs interface
>
> echo 1 > /debug/readahead/stats_enable
> echo 0 > /debug/readahead/stats_enable
>
> Example output:
> (taken from a fresh booted NFS-ROOT console box with rsize=524288)
>
> $ cat /debug/readahead/stats
> pattern readahead eof_hit cache_hit io sync_io mmap_io meta_io size async_size io_size
> initial 702 511 0 692 692 0 0 2 0 2
> subsequent 7 0 1 7 1 1 0 23 22 23
> context 160 161 0 2 0 1 0 0 0 16
> around 184 184 177 184 184 184 0 58 0 53
> backwards 2 0 2 2 2 0 0 4 0 3
> fadvise 2593 47 8 2588 2588 0 0 1 0 1
> oversize 0 0 0 0 0 0 0 0 0 0
> random 45 20 0 44 44 0 0 1 0 1
> all 3697 923 188 3519 3511 186 0 4 0 4
>
> The two most important columns are
> - io number of readahead IO
> - io_size average readahead IO size
>
> CC: Ingo Molnar <mingo@xxxxxxx>
> CC: Jens Axboe <axboe@xxxxxxxxx>
> CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Looks good to me.
Acked-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/Kconfig | 15 +++
> mm/readahead.c | 202 +++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 217 insertions(+)
>
> This switches to the percpu_counter facilities.
>
> --- linux-next.orig/mm/readahead.c 2011-12-23 20:29:14.000000000 +0800
> +++ linux-next/mm/readahead.c 2011-12-23 20:50:04.000000000 +0800
> @@ -33,6 +33,202 @@ EXPORT_SYMBOL_GPL(file_ra_state_init);
>
> #define list_to_page(head) (list_entry((head)->prev, struct page, lru))
>
> +#ifdef CONFIG_READAHEAD_STATS
> +#include <linux/ftrace_event.h>
> +#include <linux/seq_file.h>
> +#include <linux/debugfs.h>
> +
> +static u32 readahead_stats_enable __read_mostly;
> +
> +static const struct trace_print_flags ra_pattern_names[] = {
> + READAHEAD_PATTERNS
> +};
> +
> +enum ra_account {
> + /* number of readaheads */
> + RA_ACCOUNT_COUNT, /* readahead request */
> + RA_ACCOUNT_EOF, /* readahead request covers EOF */
> + RA_ACCOUNT_CACHE_HIT, /* readahead request covers some cached pages */
> + RA_ACCOUNT_IOCOUNT, /* readahead IO */
> + RA_ACCOUNT_SYNC, /* readahead IO that is synchronous */
> + RA_ACCOUNT_MMAP, /* readahead IO by mmap page faults */
> + RA_ACCOUNT_METADATA, /* readahead IO on metadata */
> + /* number of readahead pages */
> + RA_ACCOUNT_SIZE, /* readahead size */
> + RA_ACCOUNT_ASYNC_SIZE, /* readahead async size */
> + RA_ACCOUNT_ACTUAL, /* readahead actual IO size */
> + /* end mark */
> + RA_ACCOUNT_MAX,
> +};
> +
> +#define RA_STAT_BATCH (INT_MAX / 2)
> +static struct percpu_counter ra_stat[RA_PATTERN_ALL][RA_ACCOUNT_MAX];
> +
> +static inline void add_ra_stat(int i, int j, s64 amount)
> +{
> + __percpu_counter_add(&ra_stat[i][j], amount, RA_STAT_BATCH);
> +}
> +
> +static inline void inc_ra_stat(int i, int j)
> +{
> + add_ra_stat(i, j, 1);
> +}
> +
> +static void readahead_stats(struct address_space *mapping,
> + pgoff_t offset,
> + unsigned long req_size,
> + bool for_mmap,
> + bool for_metadata,
> + enum readahead_pattern pattern,
> + pgoff_t start,
> + unsigned long size,
> + unsigned long async_size,
> + int actual)
> +{
> + pgoff_t eof = ((i_size_read(mapping->host)-1) >> PAGE_CACHE_SHIFT) + 1;
> +
> + inc_ra_stat(pattern, RA_ACCOUNT_COUNT);
> + add_ra_stat(pattern, RA_ACCOUNT_SIZE, size);
> + add_ra_stat(pattern, RA_ACCOUNT_ASYNC_SIZE, async_size);
> + add_ra_stat(pattern, RA_ACCOUNT_ACTUAL, actual);
> +
> + if (start + size >= eof)
> + inc_ra_stat(pattern, RA_ACCOUNT_EOF);
> + if (actual < size)
> + inc_ra_stat(pattern, RA_ACCOUNT_CACHE_HIT);
> +
> + if (actual) {
> + inc_ra_stat(pattern, RA_ACCOUNT_IOCOUNT);
> +
> + if (start <= offset && offset < start + size)
> + inc_ra_stat(pattern, RA_ACCOUNT_SYNC);
> +
> + if (for_mmap)
> + inc_ra_stat(pattern, RA_ACCOUNT_MMAP);
> + if (for_metadata)
> + inc_ra_stat(pattern, RA_ACCOUNT_METADATA);
> + }
> +}
> +
> +static void readahead_stats_reset(void)
> +{
> + int i, j;
> +
> + for (i = 0; i < RA_PATTERN_ALL; i++)
> + for (j = 0; j < RA_ACCOUNT_MAX; j++)
> + percpu_counter_set(&ra_stat[i][j], 0);
> +}
> +
> +static void
> +readahead_stats_sum(long long ra_stats[RA_PATTERN_MAX][RA_ACCOUNT_MAX])
> +{
> + int i, j;
> +
> + for (i = 0; i < RA_PATTERN_ALL; i++)
> + for (j = 0; j < RA_ACCOUNT_MAX; j++) {
> + s64 n = percpu_counter_sum(&ra_stat[i][j]);
> + ra_stats[i][j] += n;
> + ra_stats[RA_PATTERN_ALL][j] += n;
> + }
> +}
> +
> +static int readahead_stats_show(struct seq_file *s, void *_)
> +{
> + long long ra_stats[RA_PATTERN_MAX][RA_ACCOUNT_MAX];
> + int i;
> +
> + seq_printf(s,
> + "%-10s %10s %10s %10s %10s %10s %10s %10s %10s %10s %10s\n",
> + "pattern", "readahead", "eof_hit", "cache_hit",
> + "io", "sync_io", "mmap_io", "meta_io",
> + "size", "async_size", "io_size");
> +
> + memset(ra_stats, 0, sizeof(ra_stats));
> + readahead_stats_sum(ra_stats);
> +
> + for (i = 0; i < RA_PATTERN_MAX; i++) {
> + unsigned long count = ra_stats[i][RA_ACCOUNT_COUNT];
> + unsigned long iocount = ra_stats[i][RA_ACCOUNT_IOCOUNT];
> + /*
> + * avoid division-by-zero
> + */
> + if (count == 0)
> + count = 1;
> + if (iocount == 0)
> + iocount = 1;
> +
> + seq_printf(s, "%-10s %10lld %10lld %10lld %10lld %10lld "
> + "%10lld %10lld %10lld %10lld %10lld\n",
> + ra_pattern_names[i].name,
> + ra_stats[i][RA_ACCOUNT_COUNT],
> + ra_stats[i][RA_ACCOUNT_EOF],
> + ra_stats[i][RA_ACCOUNT_CACHE_HIT],
> + ra_stats[i][RA_ACCOUNT_IOCOUNT],
> + ra_stats[i][RA_ACCOUNT_SYNC],
> + ra_stats[i][RA_ACCOUNT_MMAP],
> + ra_stats[i][RA_ACCOUNT_METADATA],
> + ra_stats[i][RA_ACCOUNT_SIZE] / count,
> + ra_stats[i][RA_ACCOUNT_ASYNC_SIZE] / count,
> + ra_stats[i][RA_ACCOUNT_ACTUAL] / iocount);
> + }
> +
> + return 0;
> +}
> +
> +static int readahead_stats_open(struct inode *inode, struct file *file)
> +{
> + return single_open(file, readahead_stats_show, NULL);
> +}
> +
> +static ssize_t readahead_stats_write(struct file *file, const char __user *buf,
> + size_t size, loff_t *offset)
> +{
> + readahead_stats_reset();
> + return size;
> +}
> +
> +static const struct file_operations readahead_stats_fops = {
> + .owner = THIS_MODULE,
> + .open = readahead_stats_open,
> + .write = readahead_stats_write,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = single_release,
> +};
> +
> +static int __init readahead_create_debugfs(void)
> +{
> + struct dentry *root;
> + struct dentry *entry;
> + int i, j;
> +
> + root = debugfs_create_dir("readahead", NULL);
> + if (!root)
> + goto out;
> +
> + entry = debugfs_create_file("stats", 0644, root,
> + NULL, &readahead_stats_fops);
> + if (!entry)
> + goto out;
> +
> + entry = debugfs_create_bool("stats_enable", 0644, root,
> + &readahead_stats_enable);
> + if (!entry)
> + goto out;
> +
> + for (i = 0; i < RA_PATTERN_ALL; i++)
> + for (j = 0; j < RA_ACCOUNT_MAX; j++)
> + percpu_counter_init(&ra_stat[i][j], 0);
> +
> + return 0;
> +out:
> + printk(KERN_ERR "readahead: failed to create debugfs entries\n");
> + return -ENOMEM;
> +}
> +
> +late_initcall(readahead_create_debugfs);
> +#endif
> +
> static inline void readahead_event(struct address_space *mapping,
> pgoff_t offset,
> unsigned long req_size,
> @@ -44,6 +240,12 @@ static inline void readahead_event(struc
> unsigned long async_size,
> int actual)
> {
> +#ifdef CONFIG_READAHEAD_STATS
> + if (readahead_stats_enable)
> + readahead_stats(mapping, offset, req_size,
> + for_mmap, for_metadata,
> + pattern, start, size, async_size, actual);
> +#endif
> trace_readahead(mapping, offset, req_size,
> pattern, start, size, async_size, actual);
> }
> --- linux-next.orig/mm/Kconfig 2011-12-23 20:28:06.000000000 +0800
> +++ linux-next/mm/Kconfig 2011-12-23 20:29:31.000000000 +0800
> @@ -396,3 +396,18 @@ config FRONTSWAP
> and swap data is stored as normal on the matching swap device.
>
> If unsure, say Y to enable frontswap.
> +
> +config READAHEAD_STATS
> + bool "Collect page cache readahead stats"
> + depends on DEBUG_FS
> + default y
> + help
> + This provides the readahead events accounting facilities.
> +
> + To do readahead accounting for a workload:
> +
> + echo 1 > /sys/kernel/debug/readahead/stats_enable
> + echo 0 > /sys/kernel/debug/readahead/stats # reset counters
> + # run the workload
> + cat /sys/kernel/debug/readahead/stats # check counters
> + echo 0 > /sys/kernel/debug/readahead/stats_enable
--
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